Proximity detector

ABSTRACT

A proximity detector processes voltages induced across the sections of at least one antenna. 
     The antenna sections are each connected to means (30, 31 and 36 to 39) for rectifying the positive and negative alternations of the alternating signal providing two first and second signals relating, one, to the &#34;peak&#34; value of the voltage induced across the section whose voltage is the highest and, the other, to the mean value of the voltage across the various sections, the first signal supplying an adder controlled by a gate and the second signals are supplied to another input of the adder led by a limiter said means being, in turn, connected to means (21, 22) for analyzing these two signals. 
     The detector may be used with elevator doors.

DESCRIPTION BACKGROUND OF THE INVENTION

The invention relates to a proximity detector whose object is to revealthe presence of an object at a certain distance from an element, as, forexample, of an intruder in the proximity of a building entrance or of anobstacle in the trajectory of a moving body such as the tool of a press.

While not exclusively, it relates more particularly to the applicationof this detector to the vertical edges of power operated doors andespecially to hoistway doors and/or doors of elevators and hoists. Inthis particular application, the object is obviously to detect thepresence of a person or of an object that might be injured while thedoor is still at a certain distance, so that, as a result of the signalemitted by this detector, is is possible to block the door and thus tointerrupt its closing or even effect its reopening if the level of thissignal exceeds a certain threshold.

For this application to the reopening of elevator doors, there alreadyexists various devices tending to limit if not to prevent damage. Inparticular:

strain detectors, which however detect the presence of the person or ofthe object only by running into it;

pneumatic feelers which, while very sensitive, are also very fragile;

photoelectric cells, whose area of sensitivity is limited to the sectorscanned by the beam of light;

radars which, in addition to being very expensive, present the drawbackof not being selective.

Proximity detectors are also known (U.S. Pat. No. 3,018,851) comprisinga very low-frequency low-energy oscillator whose emission point isgrounded so as to emit a signal of constant amplitude and frequency,

at least one receiving antenna, divided into several independentsections, mounted on the part of the element whose approach is beingmonitored but located outside the direct radiation field of the elementsthat surround this part and which are grounded but which maintain anunvarying distance from said part, and

a processing circuit for the voltage induced in each section of thereceiving antenna by the waves reflected and radiated by the bodies thatsurround the antenna, so as to emit a final signal whose intensity willbe modified by the presence of a foreign object in proximity of saidantenna.

Detectors of this type operate by reading differences in the capacitivecoupling to the ground of each antenna section and are well suited tosolve the problem of detecting an obstacle to the closing of the doors.Unfortunately, in detectors of this type known to date, the processingof the signals emitted by the antenna sections operates by balancing abridge circuit (U.S. Pat. Nos. 3,018,851 and 2,720,284), as a result ofwhich the system is very unstable and requires complex adjustment. Thatis why one result that the present invention achieves is a very stabledetector, which is simple to adjust, inexpensive and easily mounted onthe element in whose proximity is to be detected the approach of anybody and, for example, on specially designed or already existing doors.

SUMMARY OF THE INVENTION

To this end, an object of this invention is a detector of the typedescribed above, in which the antenna sections are each connected tomeans for rectifying the positive and negative alternations of thealternating signal received by it. Each of these means delivers intodistinct circuits two first and second signals. All of the circuits ofthe first signals, which are emitted by the positive alternations, areconnected to one of the inputs of an adder which is controlled by a gateactually transmitting to this input only the first signal emitted by thesection whose voltage is highest. All the circuits of the secondsignals, which are emitted by the negative alternations, are connectedto the other input of the adder control led by a limiter, so as totransmit to this input only the sum of the second signals divided by thenumber of sections.

Another object of this invention is the structural elements equippedwith this detector.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be clearly understood from the followingdescription of a non-restrictive example illustrated by the accompanyingdrawings of a preferred embodiment thereof applied to an elevator doorin which:

FIG. 1 is a block diagram of the assembly receiving the signals;

FIG. 2 is a symbolic diagram of a processing circuit for the signalsemitted by the antennas; and

FIG. 3 is a cross-section view of the door edges equipped with thedetector.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings, it can be seen that the device comprises anoscillator 1 of very low frequency (FIG. 3), such as 8 kilohertz, andlow energy, whose emission point 2 is connected to the ground 3 so as toemit to the latter a sinusoidal signal of constant amplitude and,secondarily, of constant frequency. As a result, any approaching person,being necessarily more or less connected to the ground, receives energywhich the device radiates to its immediate surroundings in the form ofelectromagnetic waves.

The same is true of any metallic object connected to the ground as, inthe present example, an elevator door 4 having panels 5, 6 grounded at7, 8. The edges 11, 12 of the panels are then equipped with a metalshield 13, 14, for example of aluminum, after insertion of a layer ofany type of known insulating material 9, 10.

Shields 13, 14 are connected at 18 to the reference voltage ofoscillator 1 by connectors 15, 16, 17. In front of each shield 13, 14thus, outside the direct radiation field of panels 5, 6 each door edgeis provided with an antenna 19, 20, divided into several independentsections, for example into six sections 19a and 19f (FIG. 2).

These antenna sections receive only reflected waves from certain bodiesand mainly waves radiated by other bodies which are more or less coupledto ground or which emit a part of their induced potential.

In the absence, within the wave field, of riders or objects and ingeneral of any foreign body, the waves thus reflected and/or radiated bythe permanently mounted parts act on the various antenna sections inproportions that remain constant.

The moment a foreign body is in the proximity of one of the antennasections, the foreign body radiates or reflects upon this section afield of higher value. This then modifies the intensity of reception ofthis antenna section and of its output signal. The closer the foreignbody, the stronger this effect.

The processing in an analyzer 21, 22 of the variations in the proportionof the output signals of the antenna sections permits the detection andevaluation of the more or less immediate proximity of the foreign body.

Before analysis, the output signals can obviously be adjusted to apredetermined level so that all are equal in the absence of foreignbodies.

In order to evaluate the distance of the object and, therefore, theurgency of intervening, the signal is fed to two logic gates 23, 24(FIG. 1) acting as triggers adjusted to different thresholds, the firstone controlling through a delay circuit 25 a blocking relay 26 for thegates, while the other one similarly controls through a delay relay 27the relay 28 that reopens the gates.

A time relay 29 detects the duration of the blocking or reopeningsignals beyond a pre-set time and activates an alarm.

In accordance with a characteristic of the present invention, theantenna sections are connected to means for the sampling of two distinctsignals, one of which relates to the peak level of the voltage inducedacross the section whose voltage is highest, and the other relates tothe mean value of the voltages in all the sections, as well as to meansfor comparing these two signals.

In the preferred embodiment, these means of sampling and analyzingcomprise means 36, 37 (FIG. 2) to rectify the positive and negativealternations of the alternating signal it receives, such as diodes.

Means 36, 37 produce signals in the distinct circuits 38, 39 which are:

a first signal "A" to "F" for the positive alternations,

a second signal "a" to "f" for the negative alternations,

where, owing to an initial adjustment, and in the absence of any foreignbody, a=A, b=B, c=C, d=D, f=F.

All the circuits 38 connected to gates 30 of the first signals, whichare produced by the positive alternations, are connected to one of theinputs 40 of the comparator 21, such as an operational amplifiercontrolled by gate 30 (FIG. 2), so as to actually transmit to input 40only the value of the first signal A, or B, or C, or D, or E, or F,emitted by the section whose voltage is the highest.

All of the circuits 39 of the second signals, which are produced bynegative alternations, are connected to the other input 41 of thecomparator 21 controlled by a limiter 31, such as a resister. Eachlimiter 31 is selected so as to pass 1/6 of the voltage normallypresent, and the mean value of the voltage of the various signals of thepresent example delivered to input 41 under normal condition is the sumof these 1/6 voltages of the signals a,b,c,d,e,f.

Comparator 21 then adds these two distinct signals and, because of theinitial adjustment described above, which is carried out in the absenceof a foreign body, and since the signals A to F and a to f of theantenna sections are adjusted to be identical, the detections of thepositive and negative alternations balance each other and the outputsignal Y is equal to zero.

For example, if the effect of external conditions is represented by x,either: ##EQU1## and, since all of the signals A to F are identical,##EQU2##

The moment a foreign body approaches, the signals received by thevarious sections are different, for example:

    a=-2, b=-2, c=-2, d=-2, e=-1, f=-1.

At the output of comparator 21, signal Y will then equal: ##EQU3##

In this preferred embodiment, gate 30 has diodes 36 which, as is known,allow only the peak value to pass, providing they are not otherwiseblocked, being connected at their bases, by a higher signal emitted byanother diode.

Because of the division of the antenna into several sections and becauseof the way the signals are processed, signal Y emitted by comparator 21has the advantage of being increased and, when equilibrium is achieved,of being practically unaffected by any conditions external to theoperation, which results in high detection stability.

In the embodiment described here involving a door composed of two movingpanels, two antennas 19, 20 are used divided into several sections but,obviously, in the case of a door having only one moving panel, therewill be but one antenna 19. However, there will be a shield on the twovertical edges defining the opening, on the edge of the mobile panel andon the edge of the fixed panel or upright, so that the upright will notradiate directly toward the antenna when the door is completely ornearly closed.

In the preferred embodiment, the metal shield forms a U-shaped channelcapping the edge of the door panel or of the upright and having anexternal fitting 32, 33 hollowed out to house the antenna and closed atthe front by a plate 34, 35 that is transparent to the electric waves.

In accordance with another characteristic of the present invention,fittings 32, 33 housing the antenna of the two panels of a door are lessthan half the width of the shield and are staggered with respect to eachother. Thus, each flanks one of the sides of the panel, and they arepositioned side by side when the door is in closed position.

What I claim is:
 1. Proximity detector for revealing the presence of abody at a certain distance from an element (5, 6) detecting the bodycomprisingan oscillator (1) whose emission point (2) is connected to theground (3) so as to transmit to the latter a signal of constantamplitude and frequency; at least one monitoring antenna (19, 20)divided into several independent sections, mounted on the part (11, 12)of said element (5, 6) whose approaches are being monitored, but locatedoutside of the direct radiation field of the elements coupled to groundwhich normally surround this part and act indirectly on said antennasections; a processing circuit for the voltages induced across eachmonitoring antenna section by the waves simultaneously reflected andradiated by the bodies normally surrounding the antenna as well as byany foreign body, said processing circuit functioning to emit a finalsignal whose intensity is modified by the existence of a foreign body inthe proximity of said antenna, the antenna sections being connected tomeans (30, 31 and 36 to 39) in said processing circuit for sampling twodistinct signals relating, one, to the "peak" value of the voltageinduced across the section whose voltage is the highest and, the other,to the mean value of the voltage across the various sections, whichsampling means is in turn connected to means (21, 22) of analyzing thesetwo signals.
 2. Detector in accordance with claim 1, said sampling andanalyzing means of said processing circuit comprising means (36, 37)connected to each of the antenna sections for rectifying the positiveand negative alternations of the alternating signal received by them,each of said means providing two signals, first and second signals, todistinct circuits (38, 39), the circuits (38) of the first signals,produced by the positive alternations, being connected to one of theinputs (40) of said analysis means (21) under the control of a gate (30)transmitting to this input only the first signal emitted by the sectionwhose voltage is the highest, all of the circuits (39) of the secondsignals, produced by the negative alternations, being connected to theother input (41) of said analysis means (21) under the control of alimiter (31) so as to transmit to this input only the sum of the secondsignals divided by the number of sections.
 3. Detector in accordancewith claim 1, applied to a door (4) having two vertical edges (11, 12)forming an opening, said edges being formed by the edges of two panels(5, 6) at least one of said panels being a moving panel, a shield(13,14) being formed by a U-shaped channel capping the edge of thecorresponding panel and carrying an external hollow fitting (32, 33) tohouse the antenna.
 4. Detector in accordance with claim 3, said fitting(32, 33) housing the antenna being at most half the width of saidchannel (13, 14) and, in a door composed of two moving panels therebeing, two hollow fittings, each flanking a distinct side of the door.